JP3397141B2 - White LED - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel semiconductor light emitting device capable of emitting white light with a single device. There is much demand for white light. White light is most suitable as a light source for illumination. White light is used as the liquid crystal backlight. The present invention relates to a semiconductor white LED that can be used for lighting, display, liquid crystal backlight, and the like.

[0002]

2. Description of the Related Art Light emitting diodes (LEDs) having a single color such as red, yellow, green and blue have already been manufactured and sold. As a red high-intensity light emitting diode (LED), one having several Cd (candela) or more is already on the market.
Red L with AlGaAs or GaAsP as the light emitting layer
It is ED. It is a low-cost LED and is used for a wide range of purposes. Green / yellowish green LEDs using GaP as a light emitting layer are also manufactured and sold. Some blue LEDs have SiC as an active layer. Blue and green have LEDs with GaInN as an active layer. Orange and yellow have elements using AlGaInP as a light emitting layer. All are inexpensive and practical LEDs. Of these, GaP and SiC are indirect transition type semiconductors and therefore have low efficiency and have not reached a candela-class output.

All of these LEDs use the band-to-band electronic transition of the material of the light emitting layer and therefore emit only monochromatic light.
That's why LEDs are monochromatic. This is natural. Monochromatic LEDs have many uses, such as display LEDs. However, monochromatic LEDs alone cannot replace all light sources. A monochromatic light source is not useful for applications such as lighting, applications such as special displays, and applications such as LCD backlights. If you use monochromatic light for illumination, all objects will appear in that color. If you use monochromatic light for the LCD backlight, you can only see the grayscale image of that color.

There is absolutely a need for a white light source that contains all colors. However, there is no semiconductor light emitting device that produces white color.
Incandescent lamps and fluorescent lamps are still widely used as illumination light sources. Incandescent light bulbs are inefficient. It also has a short life. Fluorescent lamps have a short life span, not just efficiency. A heavy item such as a ballast is required. The size is too large. There are such difficulties.

It is desired for the white light source to have a small size, a simple peripheral circuit, a long life, good luminous efficiency, and low cost.
It seems that there are only semiconductor light emitting devices to satisfy these requirements. However, as described above, since the semiconductor light emitting device uses the electronic transition between band gaps, it is inevitably only monochromatic light. The semiconductor device alone cannot generate white light.

[0006]

It would be possible to make white LEDs by using LEDs of the three primary colors blue, green and red. Blue LEDs using GaInN have become commercially available, and LEDs of three primary colors are available. However, combining three light emitting elements results in high cost.
Not only the product cost but also the electric power is tripled, so it cannot be said that the efficiency is good. It is also necessary to adjust the balance between the three primary colors. The circuit must be complicated. It is also disadvantageous in terms of size. There is little benefit in combining white LEDs by combining a plurality of LEDs in this way. After all single LE
I want to get white in D.

An LED using GaInN as an active layer and a sapphire substrate as a GaInN-based LED or simply GaN
System LED. An attempt of a white LED in which a GaInN-based LED and a YAG-based phosphor are combined has been proposed.
For example, there is a white semiconductor light emitting element introduced in the following document. "Optical functional material manual" Editing of optical functional material manual, edited by the secretariat, published by Optronics, p457, 19
June 1997

This device has a GaInN active layer.
It has a structure in which an N-based LED chip is embedded in a YAG fluorescent material that emits yellow light. This is shown in FIG. A first lead 2 and a second lead 3 are fixed in a resin transparent mold 1. The upper portion of the first lead 2 has a Γ shape, and the depression 4 is formed. A GaN-based LED chip 5 having a GaInN active layer is fixed in the recess 4. A yellow YAG phosphor 6 is filled in the recess 4 so as to completely cover the LED 5. An anode electrode and a cathode electrode are provided on the upper surface of the GaN-based LED, and these are connected to the leads 2 and 3 by the wires 7 and 8.

Since a normal light emitting element or light receiving element uses a conductive substrate, the bottom surface of the chip serves as an electrode and is directly attached to the lead.
Therefore, one wire is enough to connect the lead to the other upper electrode. However, for a GaN-based blue LED, GaN or GaInN layers are laminated on a sapphire substrate. Since sapphire is an insulator, the bottom cannot be the cathode.
Therefore, an n-electrode (cathode) and a p-electrode (anode) are formed side by side on the upper surface of the chip. So you need two wires. GaN-based LE when current is passed from the anode to the cathode
D emits a blue color. A part of the blue color is directly transmitted through the YAG phosphor and emitted to the outside. The rest is absorbed by the phosphor 6 and emits yellow light having a longer wavelength. Blue and yellow lights overlap. The combined light is white. So this is Ga
The blue color of the N-based LED and the fluorescent light excited by the blue color are superimposed on each other to produce white color.

The light emission of the LED is a positive light emission due to the band transition of electrons. The phosphor absorbs the light and emits light when an internal electron is excited from the ground band to an upper band and the electron falls to the ground band through a level called an emission center. Naturally, this excited light emission emits light whose energy is lower than that of the LED. Surrounding the LED with a suitable phosphor allows the LED's intrinsic light and longer wavelength fluorescence to be emitted. The YAG phosphor emits just yellow light, and is said to be white when combined with the blue color of the LED. In visible light, blue has a short wavelength and high energy. This is possible because there is a blue light emitting element.

FIG. 2 shows the emission spectrum of the GaInN / YAG light emitting device. The horizontal axis represents wavelength and the vertical axis represents light intensity (arbitrary scale). The sharp peak at 460 nm is GaInN.
This is due to the light of the system LED. The wide peak around 550 nm is the fluorescence from the YAG phosphor. The naked eye cannot separate and observe the colors, so it looks like white light emission.

However, the GaInN / YAG light emitting device has some drawbacks. An extra YAG phosphor, which is a completely different material from the GaInN LED, is required. This is the first difficulty. Since the YAG phosphor having poor transparency is filled on the chip, most of the light from the LED is absorbed.
With only the blue GaN LED used for this, the brightness is 1C.
It has excellent characteristics such as d or more and external quantum efficiency of 5% or more. However, GaInN / YAG has a brightness of 0.5.
Cd and external quantum efficiency are only about 3.5%. The brightness is reduced because the YAG phosphor absorbs light. Moreover, the light conversion efficiency of the YAG phosphor is low at about 10%. Therefore, the fluorescent material layer must be made thicker in order to obtain a warm white color in which yellow is dominant. Then, absorption is further increased, and both brightness and efficiency are reduced. This is the second difficulty. The third difficulty is that it requires a complicated manufacturing process.

[0013]

The present invention proposes a white LED having a simple structure in which a GaN substrate containing a fluorescent center and a GaInN-based blue light emitting element are simply combined. When a p-type GaInN thin film is grown on an n-type GaN substrate having a fluorescent center, it becomes a blue LED that emits light at 400 nm to 500 nm. The present invention skillfully utilizes this structure to fabricate white LEDs. The GaN substrate and a GaInN-based LED that lattice-matches the GaN substrate are simply combined to form an extremely simple structure. The phosphor is unnecessary, and the GaN substrate also serves as the phosphor. GaInN can be epitaxially grown on GaN, and the materials of the same system are used as a light emitter and a phosphor. A blue LED was originally made into a white LED with some modifications. GaInN
A semiconductor crystal substrate is indispensable for a blue light emitting device.
The substrate is simply doped with a fluorescent center so that it emits fluorescence. The originally required substrate is used instead of the phosphor. It is a very clever idea.

Conventionally, it has been considered that a large GaN substrate with few defects cannot be manufactured. GaN itself does not easily melt even at high temperature and high pressure, and the Czochralski method and Bridgman method cannot be used. Thus, conventionally, GaInN LEDs have been formed on sapphire substrates. The present invention cannot be implemented without a GaN substrate. In recent years, it has become possible to manufacture a GaN substrate by a melt growth method or a vapor phase growth method. This enabled the present invention. The melt growth method uses Ga
This is a method of melting aN and applying pressure and heat to form a Ga-GaN melt, and growing a GaN single crystal. You can make small crystals.

In the vapor phase epitaxy method, a mask having a large number of dot-shaped holes and linear holes is provided on a (111) GaAs substrate, and GaN is vapor-phase grown at a low temperature through the mask to form a buffer layer. An epitaxial layer is grown thickly on it and the GaAs substrate is removed to make a large GaN single crystal substrate. In other words, the substrate was grown using the thin film growth method. HVPE (halide vapor phase epitaxy) method, MOC (organic metal chloride vapor phase epitaxy) method, MOCVD (organic metal CV)
D method) method, etc. A Ga metal melt is placed in an HVPE hot wall type furnace, and hydrogen and HCl gas are blown to form GaCl to react with ammonia near the substrate.
aN is synthesized. MOC is an organic metal such as TMG,
React with H ₂ + HCl gas in a hot wall furnace
Cl is synthesized, and this is reacted with ammonia NH ₃ to produce G
Make aN. In MOCVD, an organic metal such as TMG is transported by H ₂ in a cold wall reactor and reacted with ammonia to form GaN. The manufacturing method of these GaN substrates is described in Japanese Patent Application No. 10-
No. 171276. It is only recently that large GaN substrates can be manufactured. The present invention uses such a GaN substrate as a starting material for a white LED.
To make.

When a GaN substrate is grown by a vapor phase growth method or a melt growth method, impurities (dopants) such as oxygen and carbon can be doped, and crystal defects (nitrogen vacancies) can be introduced. Impurities such as oxygen and carbon or crystal defects such as nitrogen vacancies are the center of fluorescence emission. 48
When light with a wavelength shorter than 0 nm is applied, it is 520 nm to 65 nm.
It produces fluorescence in a wide range of 0 nm. This emission center can be called a fluorescence emission center or simply a fluorescence center. The center wavelength of fluorescence emission and the half width of emission spectrum are
It can be adjusted by the type of dopant (oxygen, carbon), the doping amount, or the amount of crystal defects (nitrogen vacancies). Fluorescence changes from yellow to red (520nm-650nm)
Since it is widely distributed, this and GaInNLED with blue added will appear. It is seen as white light by combining with the naked eye. White light is synthesized from two lights, such as white light = GaInN blue + GaN fluorescence.

That is, the device of the present invention comprises two parts: (1) GaInN LED ... Blue light emission (400 to 500 nm) due to band-to-band transition (2) GaN substrate ... Yellow to red fluorescence (fluorescence: 520 to 520)
650 nm) in combination. The GaN substrate may be n-type or p-type. In either case, a pn junction is formed in the epitaxial growth layer. The epitaxial growth layer has a light emitting structure. The substrate becomes a phosphor.

The advantage of this device is its simplicity.
Approximately a light emitting device is one in which an active layer is formed on some substrate, and the substrate is always present. In an ordinary device, the substrate simply holds the active layer and allows a current to flow, and is passive. However, in the present invention, the substrate itself is skillfully used as a fluorescent light emitting layer. Therefore, the white LED of the present invention is made of GaN in the GaInN blue LED.
Impurities (dopants) that cause fluorescence emission centers on the substrate
And only lattice defects are added, and only one process is added. It does not add different materials.

There are various kinds of white. When blue is dominant, it becomes cold white, and when red is dominant, it becomes warm. If the GaN substrate is thick, the blue color of GaInNLED is absorbed and reduced, and the yellow color of fluorescence emission becomes dominant. Ga
If the N substrate is thin, the blue color of GaInN LED is dominant and the fluorescence emission becomes weak. The intensity of fluorescence emission can be adjusted by changing the thickness of the GaN substrate. That is, the ratio of the fluorescence emission to the blue emission from the LED can be changed depending on the substrate thickness. However, the substrate thickness is limited by other conditions. If the thickness is 50 μm or less, the rate of damage increases in the subsequent process. Yield also decreases and cost increases. On the contrary, when the substrate thickness is 2 mm or more, the size of the LED becomes too large. In addition, the proportion of yellow light increases excessively, and it is no longer white. Therefore, the substrate thickness is 50 μm-2 m
It is about m.

As described above, the central wavelength of fluorescence emission can be changed by adjusting the dopant type, concentration and defect density. The ratio of fluorescence can be changed depending on the substrate thickness. Therefore, by freely adjusting the parameters such as the type of impurities, the concentration, the defect density, and the substrate thickness, it is possible to obtain an arbitrary white color from a warm white color to a cold white color.

There are several options for the geometric arrangement. The same arrangement (upright) as that of a conventional LED in which the substrate is on the bottom and the thin film is on the top is also possible. On the contrary, it is also possible to arrange an inverted structure (episide down) with the thin film on the bottom and the substrate on the top. It is also possible to adopt a structure that prevents only the blue color from being emitted to the outside.

The electrodes of the LED are formed on the epitaxial side and the back side of the substrate respectively (in the case of an n-type substrate, an n-electrode on the back side and on the epitaxial side are p-electrodes; on a p-type substrate, the back-side p-electrode, the epitaxial side). N electrode). The electrode on the surface to be attached to the stem may be an electrode that covers the entire surface, but the electrode on the light emission side must have a wide opening.

When mounting by episide down, it is desirable to have the following structure. It is necessary to make the electrode on the epitaxial side as large as possible in order not to let blue and blue-green from the light emitting layer go outside the chip. The electrode on the epitaxial side is preferably an electrode that covers the entire surface of the chip or 80% or more of the entire surface of the chip. On the contrary, since the substrate side is the light emitting side, it is necessary to reduce the electrode area. It may be either ring-shaped or dot-shaped, but for a standard chip size of 0.25 mm × 0.25 mm, the area ratio is 40% or less. More preferably, it should be 16% or less.

When an n-type GaN substrate is used, episide-down allows a large-area p-electrode to be formed in the p-type epitaxial layer where it is difficult to achieve a low specific resistance, and contact resistance can be reduced. N-type GaN may be a ring-shaped narrow electrode because it is easy to reduce the resistance. In this way, an electrically favorable structure is obtained. Since the GaN substrate is a single crystal, it has higher transparency than the YAG phosphor. The efficiency of converting blue and blue-green light into yellow light is 15% higher than that of YAG phosphor. Since both the transparency and the conversion efficiency are high, the GaInN / GaN LED of the present invention is a white LED having a higher brightness than the GaInN / YAG according to the conventional example. Also, simply by changing the thickness of the GaN substrate,
It is possible to obtain warm to cold white light. Since the transparency is high, the brightness does not decrease even if the thickness is increased.

Further, it is not necessary to embed the fluorescent material. A high brightness white LED can be manufactured by a simple process. The GaN substrate can be conductive. The manufacturing process is simplified because there is one less wire bonding than the element on the conventional sapphire substrate (insulator). Low cost white LED can be made.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION (1) Upright GaN White LED FIG. 3 shows an example of the structure of a white LED according to the present invention.
FIG. 3A shows a vertical sectional view, and FIG. 3B shows a sectional view of only the chip. The leads 12, 13 and the LED chip 15 are embedded in the transparent mold 11. Such a structure is compatible with conventional LEDs. The transparent mold is the cheapest LED package. Of course, it can be housed in a metal can type package. Packages and leads can be freely selected according to the purpose. Γ type lead 12
The top 14 has no dent and has a flat surface. The GaInNLED 15 is fixed upright on the flat surface 14. This LED 15 is composed of a GaN substrate 16 having impurities (oxygen, carbon) serving as fluorescent emission centers, crystal defects (nitrogen vacancies), and a light emitting structure (thin film) 17 epitaxially grown thereon.

The light emitting structure 17 is a GaInN thin film and is made of p
Includes n-junction. The epitaxial light emitting structure 17 is a laminated body of thin films composed mainly of GaN, and has a ring-shaped or small-area p electrode on the top having a pn junction. It should not exceed 40% of the total area so as not to block light. The p-electrode is connected to the lead 13 by the wire 18. The n-electrode on the substrate side is directly connected to the lead 12. Only one wire is required. The lead 12 serves as a cathode and the lead 13 serves as an anode. A bandgap transition occurs by passing a current through the pn junction, and light E of 400 nm to 500 nm is emitted.
Part of it goes down and enters the substrate. Here, the GaN substrate has oxygen, carbon, or nitrogen vacancies, and absorbs blue light to
It fluoresces between 20 and 650 nm. The fluorescence emission F in the substrate is reflected on the bottom surface or directly goes over the thin film 17 to the outside. The mixed light of the LED light E and the fluorescent light F goes out to the outside and appears as white light W (W = E + F). This is an upright structure in which the substrate 16 is bonded to the lead surface 14. This is true of all normal LEDs. But this is LE
The ratio of D light E always exceeds 50%, and fluorescence emission becomes weak.

(2) Inverted GaN White LED FIG. 4 shows an example of the structure of the inverted white LED according to the present invention. FIG. 4A shows a vertical sectional view, and FIG. 4B shows a sectional view of only the chip. Inside the transparent mold 21, the lead 2
2, 23 and the LED chip 25 are embedded. Such a structure is compatible with conventional LEDs. The top 24 of the Γ-shaped lead 22 has no depression. It is a flat surface. The GaInNLED 25 is fixed on the lead top portion 24. L
ED25 is a G having an impurity and a defect which serve as a fluorescence emission center
It is composed of an aN substrate 26 and a light emitting structure (GaInN-based thin film) 27 epitaxially grown thereon. The epitaxial light emitting structure (thin film) 27 is a GaInN thin film and includes a pn junction. This LED is fixed to the lead surface 24 in the opposite direction. When using an n-type GaN substrate, there is a p-electrode on the thin film surface, which is directly bonded to the lead surface 24 (stem). The electrode attached to the stem is 80% of the chip area
It may be 100%. There is a ring-shaped or small-area n electrode on the GaN substrate side. This is 40% of the chip area
The area is as follows. The n-electrode is connected to the lead 23 by the wire 28. After all, one wire is enough. In this case, the lead 23 serves as a cathode and the lead 22 serves as an anode. Of course, when using a p-type substrate, the cathode and anode are reversed.

A band gap transition is caused by passing a current through the leads 22 to 23, and the epitaxial thin film 2
7 emits light E of 400 nm to 500 nm. All goes up and enters the board. The transmitted light goes out as blue light. Part of the light is absorbed and promotes fluorescence emission by the fluorescence center in the GaN substrate. The fluorescence emission F in the substrate also goes upward. Both the LED light emission E and the fluorescence light emission F go upward.
The two different types of light are mixed and become white. With this structure, fluorescence increases in proportion to the thickness of the substrate. 50% fluorescence
It is easy to do the above. Easy to control the color tone of white light. However, it is necessary to note that the normal LED and the anode and cathode pins are opposite.

(3) Inverted shield type GaN white LED In FIG. 4, the blue light and the blue-green light emitted from the thin film 27 substantially parallel to the substrate surface cannot be mixed with the fluorescent light because they do not pass through the substrate, and the blue light is blue. It just becomes. Color unevenness occurs when viewed from the side. In order to avoid this, the lead shape may be devised. FIG. 5 shows an example of the structure of the inverted shield type white LED according to the present invention. FIG. 5A shows a vertical sectional view, and FIG. 5B shows a sectional view of only the chip. Leads 32 and 33 and an LED chip 35 are embedded in the transparent mold 31. Such a structure is compatible with conventional LEDs. A deep recess 39 is formed in the top portion 34 of the Γ type lead 32. Ga at the bottom of the deep recess 39 of the lead top 34
The InNLED 35 is fixed upside down with the light emitting structure facing down. The area of the upper opening viewed from the LED 35 is narrow so that the light does not go out to the side.

The LED 35 comprises a GaN substrate 36 having a dopant serving as a fluorescent emission center and a light emitting structure (GaInN type thin film) 37 epitaxially grown thereon. The epitaxial light emitting structure (thin film) 37 is a GaInN thin film and includes a pn junction. This LED is fixed in the opposite direction on the bottom 34 of the recess 39. An electrode having an area of 80% to 100% of the entire surface is provided on the upper surface of the thin film 37, and this is directly bonded to the bottom surface of the recess of the lead 32. When using an n-type substrate, the thin film electrode is a p electrode. There is a ring-shaped or small-area electrode on the GaN substrate side. 40% or less of the total area. For an n-type substrate this is the n-electrode. The n-electrode is connected to the lead 33 by the wire 38. After all, one wire is enough. Also in this case, the lead 33 serves as a cathode and the lead 32 serves as an anode. A ring-shaped reflector 40 is joined to the upper surface of the recess 39. In the case of a p-type substrate, the electrode on the substrate side is the p electrode and the electrode on the light emitting mechanism (thin film) side is the n electrode.

The epitaxial thin film 37 emits light E of 400 nm to 500 nm by passing a current. All goes up and enters the board. The transmitted light goes out as blue light. Part of the light is absorbed and causes fluorescence emission by the fluorescence center of the GaN substrate. Fluorescence emission F in the substrate
(520 nm to 650 nm) also goes upward. Both the LED light emission E and the fluorescence light emission F go upward. The combination of both gives a white color. All light emitted obliquely to the surface is blocked by the hollow wall surface. Only the light emitted perpendicular to the surface can go upwards and go out from the depression. This will be a directional LED.

(4) Inverted substrate shielding type GaN white LED Since there is no light emitted sideways in FIG. 5, it always becomes white light. That's good, but it has the drawback of being too directional. An LED with less directivity may be required. In addition, the structure shown in FIG. 5 has a complicated lead shape and is difficult to mount on an LED chip. LED with low directivity and no leakage of blue and blue-green
Will be described with reference to FIG. In this, the GaN substrate itself is provided with a concave shape and the light emitting structure is embedded in the substrate.

FIG. 6A shows a vertical sectional view, and FIG. 6B shows a sectional view of only the chip. Leads 42 and 43 and an LED chip 45 are embedded in the transparent mold 41. An LED with a unique shape is formed on the top portion 44 of the Γ type lead 42.
Chip 45 is bonded in the opposite direction. The center of the LED 45 is a deep recess 49, and the GaInN-based epitaxial light emitting structure 47 is formed therein. That is, the epitaxial thin film 47 is surrounded by the GaN substrate 46. All light emitted from the epitaxial thin film 47 passes through the substrate 46.

An insulating layer 50 and a GaN layer 5 are provided around the substrate.
There is one. The LED 45 is bonded to the lead surface 44 by the GaN layer 51. However, due to the insulating layer 50, no current flows from the lead surface 44 to the device. There is a ridge 52 at the center of the lead surface 44. The ridge 52 is fixed in contact with the p-electrode of the epitaxial light emitting layer. This electrically connects the p-electrode and the lead 42. The bottom side of the GaN substrate 46 is on top. There is a ring-shaped or small area electrode on the bottom surface. If it is an n-type substrate, it is an n-electrode. The n-electrode is connected to the lead 43 by the wire 48. Lead 4
2 is an anode and the lead 43 is a cathode.

By passing a current, the epitaxial thin film 47 emits light E of 400 nm to 500 nm. All of the light traveling upward and the light traveling laterally enter the peripheral substrate 46.
The transmitted light goes out as blue light. Part of the light is absorbed by the substrate 46 and causes fluorescence emission due to fluorescent centers such as impurities and defects in the GaN substrate. Both the LED emission E and the fluorescence F go upward and sideward. Together, they are white. Not only the light perpendicular to the substrate surface but also light emitted obliquely or laterally becomes white light. It becomes an LED with no directivity. It has a wider range of uses.

[0037]

EXAMPLES Example 1 (Vapor-grown GaN substrate, GaIn
N active layer, upright)] GaN single crystal is grown by vapor phase growth (HVPE, MOC, MOCVD method) or melt growth method as described above. The GaN free-standing film is used as a substrate. The GaN substrate has a defect such as a dopant such as oxygen or carbon or a nitrogen vacancy. Oxygen, carbon, and nitrogen vacancies serve as fluorescent centers. The thickness of the GaN substrate is 5
About 0 μm to 2000 μm is preferable. G on the GaN substrate
A crystalline thin film of aInN is epitaxially grown. For example, epitaxial growth can be performed by MOCVD.

FIG. 7 shows a GaN epitaxial wafer-60.
Shows the structure of. On the n-type GaN substrate 62, the n-type GaN buffer layer 63, the n-type AlGaN cladding layer 64, and GaI.
An nN active layer 65, a p-type AlGaN cladding layer 66, and a p-type GaN contact layer 67 are provided. In the epitaxial layer, Mg was used as the p-type dopant and Si was used as the n-type dopant. A more specific composition is shown.

(1) n-type GaN substrate 62 (2) n-type GaN buffer layer 63 (3) n-type Al _0.20 Ga _0.80 N clad layer 64 (4) Zn-doped Ga _0.88 In _0.12 N active layer 65 (5) p-type Al _0.20 Ga _0.80 N cladding layer 66 (6) p-type GaN contact layer 67

The contact layer is in ohmic contact with the p-electrode and needs to have a low resistance, so that the p-type concentration is high. AlGaN
The clad layer has a wide band gap and has a function of confining carriers in the active layer. The GaInN active layer is thin I
An nN film and a GaN film are alternately laminated in multiple layers.

A p-electrode made of Pd / Au was formed on the p-type contact layer of this epitaxial wafer. An n electrode of In was formed on the n-type GaN on the back surface. In / TiAu can also be used for the n-electrode. Photolithography is used to form the pattern electrodes. The electrode-formed epitaxial wafer was cut into a 300 μm × 300 μm square size and fixed to the stem 14 of the lead 12 as shown in FIG. The n electrode was on the bottom and the p electrode was on the top. That is, the GaN substrate 16 contacts the stem 14. The p-electrode was attached to the other lead 13 by a wire. These were molded with transparent resin.

This LED was measured in the constant current mode. A bright white light was emitted. Typical brightness was 1.5 Cd for a drive current of 20 mA. This LE in Figure 8
The emission spectrum of D is shown. As designed, the LED emission from the epitaxial light emitting layer having a sharp peak at 430 nm is combined with the fluorescent emission from the broad GaN substrate having a blunt peak at 550 nm. The combined light is white. It was a warm white with a little yellow.

[Embodiment 2] GaN Substrate of Melt Growth Method, Inverted, Three Types of Substrate Thickness] Three types of GaN substrates having different thicknesses prepared by the melt growth method were prepared. Thickness is 100μ
m, 500 μm, 1 mm. A homoepitaxial structure similar to that of the first embodiment is MOCVD-formed on the GaN substrate.
It was produced by the method. It has the structure of FIG. 7, the p-type dopant is Mg, and the n-type dopant is Si.

(1) n-type GaN substrate 62 (2) n-type GaN buffer layer 63 (3) n-type Al _0.20 Ga _0.80 N clad layer 64 (4) Zn-doped Ga _0.88 In _0.12 N active layer 65 (5) p Type Al _0.20 Ga _0.80 N cladding layer 66 (6) p-type GaN contact layer 67

A p-electrode Pd is formed on the p-type GaN contact layer.
/ Au is provided. The p electrode is formed on the entire epitaxial surface. 100 μm × 1 on the bottom surface of the n-type GaN substrate
An n electrode of In having a thickness of 00 μm was provided. The tip coverage of the p-electrode is 100% and the tip coverage of the n-electrode is 11%.
This was cut into a 300 μm × 300 μm square chip and attached to the stem with the back surface facing upward as shown in FIG. It is also called episide down because the epitaxial surface is on the bottom. The p-electrode is attached directly to the stem. Only the n-electrode is connected to the stem by wire. This was molded with transparent resin.

When this LED was made to emit light in a constant current mode, white light with high brightness could be obtained. L of Example 1
The ED showed white color unevenness, but this light receiving element does not have such unevenness in the direction perpendicular to the element surface. This is because the light emitted in the vertical direction, which is episide down, is a mixture of fluorescence and LED emission. Typical brightness is current 2
It was 1.5-2 Cd at 0 mA. Substrate thickness (100
The feeling of white is different depending on μm, 500 μm, 1 mm). (C) LED having a thickness of 100 μm ... white having a bluish cold color tone (D) LED having a thickness of 500 μm ... neutral white (E) LED having a thickness of 1000 μm ... a fairly warm yellowish white tone. FIG. 9 shows the chromaticity C, D, E of each white light emission in chromaticity coordinates.

The chromaticity diagram is obtained by digitizing the stimulus values (stimulation amounts felt by the three types of human visual sense organs) for the three primary colors red, green, and blue for general visible light source colors or object colors. , Is a diagram devised for displaying on plane coordinates. In the emission spectrum of a certain light source, when the stimulus amount corresponding to red is x, the stimulus amount corresponding to green is y, and the stimulus amount corresponding to blue is z, these are normalized by the total stimulus amount, X = The plane coordinates defined by x / (x + y + z) and Y = y / (x + y + z) are the chromaticity diagram shown in FIG. In this coordinate system, a color having any spectrum is represented as one point on the coordinate. Of this, 400 nm to 67
Monochromatic light in the range up to 5 nm draws a Λ type curve in the figure. All other colors are composite lights of these monochromatic lights, and can be represented by points inside the Λ-shaped curve in the figure. The white light is the part surrounded by the broken line near the center. It is assumed that the two colors P and Q are taken in this two-dimensional coordinate. The mixed color of these arbitrary ratios is represented as a point on the line segment connecting the two points PQ.

In FIG. 9, point A indicates light emission from only the LED light emitting structure having a peak at 460 nm. Since it has good color purity, it is located at the corner of the chromaticity diagram curve. B point is 580
It shows the chromaticity of fluorescence emission centered at nm. Since it is a broad peak and contains various lights, it is inside the Λ curve. The light obtained by combining the light at the point A and the light at the point B is on the straight line AB. When the GaN substrate is thin, the fluorescence becomes weaker, which depends on the A side. When the substrate is thick, the fluorescence becomes strong and depends on the B side.

Point C: The GaN substrate has a thickness of 100 μm. Closest to point A. Point D: The GaN substrate thickness is 500 μm. It is in the middle. Point E: The GaN substrate thickness is 1000 μm (1 mm). Closest to point B. It is also possible to express these white colors by the tone temperature. Point C ... Cold white with a little blue color and a color temperature of 8000K
degree. Point D: Neutral white with a color temperature of about 5000K. Point E: Warm white with a strong yellow color temperature of about 3000K. By changing the thickness of the substrate in this way, white with different color tones can be obtained. This is the case when the impurity concentration of the substrate is constant.

It was also found that when the impurity concentration of the substrate is changed, the absorption coefficient of the substrate changes, and the relationship between the substrate thickness and the color tone of the LED changes from the above relationship. G of active layer
The emission wavelength by varying the composition x of a _1-x In x N can vary between 40 nm to 500 nm. It was also found that white light can be obtained by optimizing the substrate thickness even when the LED emission wavelength is changed within this range.

[Embodiment 3] Inverted, Reflector] In the second embodiment, the LED is mounted on the stem upside down. Therefore, it is a uniform white color as seen from above. However, when viewed from the side of the chip, there is an angle at which only blue is emitted. Therefore, a recess was provided in the stem and a chip was mounted in the recess. This is shown in FIG. The bottom surface of the recess 39 was mirror-finished.
The chip was inverted and attached to the recess 39. In this way, all the light emitted to the side is blocked by the wall surface of the recess 39 and is not exposed to the outside. The reflector 40 further narrows the opening. Light comes out only above.

Light emitted from the epitaxial thin film must pass through the GaN substrate 36 in order to be emitted upward. Be sure to mix blue light with yellow fluorescent light. In this way, an LED emitting uniform white light could be obtained. The mounting surface 34 of the stem is mirror-finished, and an aluminum thin piece is used as a reflection plate. Since blue light is reflected and enters the GaN substrate, the yellow-orange intensity is increased by the reflection. Due to the reflector and the concave structure, the directivity was high. Brightness is 1.8-2.5C due to reflection
It was increased to d.

[Embodiment 4] Inverted, selective growth] In the third embodiment, the recess is formed in the stem, and the LED is mounted upside down in the recess. Light comes out only upward. Strong directivity and high brightness. However, it is difficult to form such a deep recess in the stem. Boost stem costs. In some cases, it may be better to provide the chip with anisotropy. This is because the chips can be easily given shape anisotropy by the wafer process.

Then, a tip stem having a shape as shown in FIG. 6 was produced. A manufacturing method will be described with reference to FIGS. A lattice-shaped SiN mask pattern 80 was formed on the GaN wafer-78. FIG. 10A shows a mask 80.
A partial cross-sectional view of a wafer on which is mounted is shown. Figure 10
(D) shows a plan view of the same thing. The white background portion of the square is the exposed portion 79 of GaN. The square portion will later become the light emitting portion. About 3 (opening) other than the mask
Etched to a depth of μm. The recess 83 is formed as shown in FIG. The portion directly below the mask 80 is undercut and remains in the shape of an inverted mesa 81. The exposed portion becomes the plane 82.

A light emitting structure was grown on the wafer having the recesses 83 by the MOCVD method as in the first to third embodiments. Selective growth occurs, a light emitting structure is formed only in the recess 82, and a single crystal epitaxial film is not formed on the mask 80. The light emitting structure is completely separated due to the undercut shape right under the mask. That is, the GaN film is not connected above and below the mask. This state is shown in FIG. Epitaxial light emitting structure 84 inside the recess 83
An electrode is provided on the mask, and the mask is used as a cutting line.
It was cut into m × 300 μm chips. An LED chip having a recess in the center is manufactured. The stem 44 of the lead 42 itself is also an irregular shape having the convex portion 52.

The tip was inverted and secured with the p-type layer in contact with the stem ridge 52. 6 (a) and 6 (b)
become that way. The n-electrode was connected to another lead 43 with a wire 48. This is because the epitaxial light emitting structure 47 is GaN
Since it is embedded in the substrate, there is no blue or blue-green leakage light. The LED emits white light uniformly for all viewing angles. This is one in which uniform light is emitted by devising the shape of the chip. This embodiment, in which the epitaxial layer is embedded in the chip, has little directivity and is a full-field type. It emits light at a wide angle and is suitable for displays.

[Embodiment 5 (Inverted, Reflector-shaped Stem)] FIG. 11 shows an embodiment in which the stem has a reflecting function. As in Examples 2 and 3, attach the stem upside down. The stem of Example 2 was flat, and the stem of Example 3 had a deep recess. The one shown in FIG. 11 is an intermediate one, and the concave portion which is not deeper than that of the third embodiment is provided in the stem. Figure 11
(A) is a plan view of the chip. (B) is a front view,
(C) is a bottom view. (D) is a front view of the element.
In this LED, not a ring electrode but a small disk-shaped n electrode 87 is provided on the back surface of the n-type GaN substrate 62. A p-electrode 88 is provided on the entire surface below the p-type contact layer 67. The top portion of the lead 89 is in the shape of a widened frame, and the epitaxial growth layer side (p electrode side) of the chip is fixed thereto. The n-electrode 87 is connected to another lead 90 by a wire 92. The entire stem, chip, wire and the like are molded with the transparent resin 93.

[0058]

According to the present invention, a GaInN thin film is epitaxially grown on a GaN substrate having a fluorescent center.
The GaInN thin film emits blue light as an LED, and when blue light passes through the substrate, it emits yellow or yellow-green fluorescent light, so that the two emit white light. It can be manufactured in a process that is almost the same as that of making a monochromatic LED. Since the substrate is not sapphire, it has cleavage and is easy to cut into chips. If the substrate is sapphire, wire bonding is required twice, but since the present invention uses a conductive GaN substrate, only one wire bonding is required. It is easy to manufacture an LED. The conductive single crystal GaN substrate has higher transparency and less absorption than the conventional YAG fluorescent material. Furthermore, the conversion efficiency of converting blue-blue-green light into yellow light is high (15% or more).
GaInN / GaNL has high transparency and high conversion efficiency.
The ED is a white LED with higher brightness than the conventional GaInN / YAGLED.

Since it is mainly composed of GaInNLED, it has a long life. It is possible to generate various white colors from warm colors to cold colors, depending on the type, concentration, and crystal defect amount of the GaN substrate. Furthermore, the color tone can be changed from warm colors to cold colors simply by changing the substrate thickness. No extra phosphor is needed. The GaN substrate itself is effectively used as a fluorescent light emitter. The semiconductor element requires a substrate, but since it is used as a yellow light emitter, the structure is simple and the manufacture is easy.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a white LED according to a conventional example in which a GaN-based LED and a YAG phosphor are combined. (A) is a whole longitudinal cross-sectional view including a package. (B) is an enlarged cross-sectional view near the LED chip.

FIG. 2 is a GaI composed of a GaN-based LED and a YAG phosphor.
The emission spectrum figure of nN / YAG white LED. The horizontal axis is the wavelength and the vertical axis is the light intensity (arbitrary scale).

FIG. 3 is a diagram showing an example of a white LED according to the first embodiment of the present invention in which an LED in which a GaN substrate and a GaInN-based thin film light emitting structure are combined is vertically fixed to a stem. (A) is a whole longitudinal cross-sectional view including a package. (B) is an enlarged cross-sectional view near the LED chip.

FIG. 4 is a diagram showing an example of a white LED according to a second embodiment of the present invention in which an LED in which a GaN substrate and a GaInN-based thin film light emitting structure are combined is inverted and fixed to a stem. (A) is a whole longitudinal cross-sectional view including a package. (B) is an enlarged cross-sectional view near the LED chip.

FIG. 5 is a diagram showing an example of a white LED according to a third embodiment of the present invention in which an LED is fixed upside down in a valley of a stem having a recess. (A) is a whole longitudinal cross-sectional view including a package. (B) is an enlarged cross section near the LED chip

FIG. 6 is a view showing an example of a white LED according to a fourth embodiment of the present invention in which an LED having a structure in which a GaN-based thin film light emitting structure is embedded in a GaN substrate is inverted and fixed to a stem having a convex portion.
(A) is a whole longitudinal cross-sectional view including a package. (B) is LE
The expanded sectional view of the D chip vicinity.

FIG. 7: LE of Example 1 having GaInN as an active layer
The figure which shows the layer structure of the epitaxial wafer of D.

FIG. 8 is an emission spectrum diagram of an LED used in the present invention having GaInN as an active layer.

FIG. 9 is a diagram showing, as C, D, and E, light emitting points of three types of LEDs having different thicknesses in the second embodiment in a chromaticity coordinate system showing chromaticity in which the horizontal axis is X and the vertical axis is Y. A is GaInNLE
D indicates light emission and B indicates fluorescence. X indicates the ratio of the red component of the three primary colors, and Y indicates the ratio of the green component of the three primary colors.

FIG. 10 is a view for explaining a wafer process for producing an LED chip of Example 4 in which a recess is formed in the center of the chip, an epitaxial light emitting structure is formed in the recess, and the light emitting structure is surrounded by a substrate. .

FIG. 11 is a diagram showing an LED chip and an LED element in Example 5 of inverted mounting. (A) is a plan view of a chip, (b) is a front view, (c) is a bottom view, and (d) is a view of a light emitting element in which a chip is attached to a lead and molded with a transparent resin.

[Explanation of symbols]

1 transparent mold 2 first lead 3 second lead 4 depressions 5 GaN InLED 6YAG phosphor 7 wires 8 wires 11 transparent mold 12 leads 13 leads 14 top 15GaInN LED 16 GaN substrate 17 Epitaxial light emitting structure (thin film) 18 wires 21 transparent mold 22 leads 23 leads 24 lead top surface 25GaInN LED 26 GaN substrate 27 Epitaxial light emitting structure (thin film) 28 wires 31 transparent mold 32 leads 33 leads 34 lead top 35GaInN LED 36 GaN substrate 37 Epitaxial light emitting structure (thin film) 38 wires 39 depressions 40 reflector 41 transparent mold 42 leads 43 leads 44 Lead top surface 45GaInNLED 46 GaN substrate 47 Epitaxial light emitting structure (thin film) 48 wires 49 depressions 50 insulating layers 51 GaN layer 52-lead uplift 60GaInN LED chip 62 n-type GaN substrate 63n-type GaN buffer layer 64n type AlGaN cladding layer 65GaInN active layer 66p type AlGaN cladding layer 67p type GaN contact layer 78 GaN substrate 79 substrate surface 80 mask 81 convex 82 bottom 83 depressions 84 Epitaxial light emitting structure 85 Non-epitaxial layer 87n electrode 88p electrode 89 leads 90 leads

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-190053 (JP, A) JP-A-10-135516 (JP, A) JP-A-10-12555 (JP, A) JP-A-5- 21847 (JP, A) JP 10-150220 (JP, A) JP 7-30153 (JP, A) JP 4-213878 (JP, A) JP 2000-12900 (JP, A) 58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 33/00

Claims (7)

(57) [Claims] 1. An n-type or p-type GaN single crystal substrate containing oxygen atoms, carbon atoms or nitrogen vacancies as fluorescent centers, and G.
a blue-blue-green light emitting structure of a mixed crystal compound mainly composed of GaInN provided by epitaxial growth on an aN single crystal substrate to include a pn junction; an n electrode or ap electrode provided on the bottom surface of a GaN substrate; A p-electrode or an n-electrode provided on the upper layer of the structure, a support mechanism for supporting the GaN substrate or the light-emitting structure, a lead for applying a current to the electrode,
It is composed of a GaN substrate, a light emitting structure, and a package that surrounds a support mechanism, and the blue or blue-green light from the light emitting structure excites the fluorescent center of the GaN substrate to emit yellow or orange light, and the blue or blue green light from the light emitting structure. A white LED characterized in that white light is obtained by combining both yellow-orange light from the fluorescent center of the GaN substrate. 2. The light emitting structure comprises a multi-layer structure containing Ga _1-x In _x N, the wavelength of light emitted from the light emitting structure is in the range of 450 nm to 510 nm, and the wavelength of fluorescent light emission from the GaN substrate. Is 520 nm-650 nm, The white LED of Claim 1 characterized by the above-mentioned. 3. The GaN substrate has a thickness of 50 μm to 2 mm.
3. The color tone of the obtained white light can be changed from a cold color system to a warm color system by adjusting the light emission wavelength from the light emitting structure by adjusting the light emission wavelength within the range. The white LED described in 1. 4. A Γ-type lead having a stem on the top as a support mechanism, wherein the substrate side is opposite to the stem and the surface having a light emitting structure is fixed to the stem surface. The white LED described in 1. 5. The support mechanism is a Γ type lead having a stem having a recess at the top, and the substrate side is opposite to the stem and the surface having a light emitting structure is fixed to the recess of the stem, and at the upper end of the recess. The white LED according to claim 3, wherein the white LED has a reflection plate and reflects a part of the blue light and the blue light emitted from the light emitting structure to irradiate the GaN substrate. 6. The GaN substrate has a recess, and G is formed at the bottom of the recess.
a _1-x In _x N light emitting structure is formed, and the light emitting structure is Ga
4. The white LED according to claim 3, wherein the white LED is surrounded by the N substrate, and the substrate side is opposite to the stem and the surface of the light emitting structure is fixed so as to contact the stem. 7. The electrode on the light emitting structure side has a total area of 8 of the substrate.
The white LED according to claim 4, 5 or 6, wherein an area of 0% to 100% is covered, and an electrode on the GaN substrate side covers an area of 40% or less of the substrate area.